Traditionally, a radar apparatus mounted on a vehicle emits a transmission wave from a transmission antenna and receives a reflected wave from a target, which reflects the emitted transmission wave, with a reception antenna to thus derive target information such as position information of the target relative to the vehicle (radar vehicle). The radar apparatus outputs the derived target information to a vehicle control device mounted on the vehicle. The vehicle control device having received the target information from the radar apparatus performs ACC (Adaptive Cruise Control) control of following up a preceding vehicle, which is a target moving in the same direction as the vehicle on an own traffic lane, towards the front of the vehicle. Also, as another example of the vehicle control, when there is a possibility that the vehicle will collide with an adjacent vehicle, which is moving in an opposite direction to the moving direction of the vehicle in an adjacent traffic lane adjacent to the own traffic lane, the vehicle control device performs PCS (Pre-Crash Safety System) control of emitting a warning sound to a user of the vehicle by using a warning device.
Here, when the vehicle control device performs the ACC or PCS control, the target that is to be controlled is a target that exists within a predetermined range from the vehicle (for example, 0 to 200 m from the vehicle). The information of the target that is to be controlled is derived by following processing that is executed by a signal processing unit of the radar apparatus. The signal processing unit performs FFT (Fast Fourier Transform) processing for a beat signal generated from a reception signal corresponding to the reflected wave from the target. By the FFT processing, data (which is hereinafter referred to as ‘FFT data’) is acquired which indicates a signal level of each frequency of the beat signal. The FFT data is data that has a level value of the beat signal at each BIN from 0 to 1023 BIN (1 BIN is about 468 Hz). The signal processing unit extracts a signal (hereinafter, referred to as ‘peak signal’) exceeding a predetermined signal level from the data of the frequency (0 to 700 BIN) corresponding to a distance of 0 to 200 m from the vehicle within a relative speed range of the target and derives the target information of the target on the basis of the peak signal. That is, the signal processing unit does not use data of the frequency of 701 to 1023 BIN corresponding to a distance beyond 200 m from the vehicle, as the target information for the vehicle control. Therefore, after the FFT processing, the signal processing unit deletes the data of the frequency of 701 to 1023 BIN of the acquired FFT data. In the meantime, Patent Document 1 discloses a technology relating to the invention.
Patent Document 1: Japanese Patent Application Publication No. 2002-122662A
However, when there is a strong reflector such as a truck, which is a target having a relatively high signal level of the reflected wave, at a distance (for example, about 461 m from the vehicle) corresponding to a frequency (for example, 1187 BIN) exceeding 1023 BIN, a peak signal (hereinafter, referred to as ‘ghost peak’) of a ghost, which is a target that does not actually exist, may be generated in the frequency range of 0 to 700 BIN of the FFT data. Specifically, due to an interference (intermodulation) between a reception signal of the strong reflector and a switching noise (for example, a noise appearing as a peak signal at the frequency of 1023 BIN) of a DC-DC converter of a power supply circuit of the radar apparatus, a ghost peak may be generated at a frequency (for example, 164 BIN) of 700 BIN or lower of the FFT data and the target information may be derived at a distance (for example, about 60 m from the vehicle) corresponding to the frequency.
As a result, the target information of the ghost peak is output from the radar apparatus to the vehicle control device and the vehicle control device performs the ACC or PCS control, so that the vehicle control may be unnecessarily performed.